Variability in Environmental Conditions Strongly Impacts Ostracod Assemblages of Lowland Springs in a Heavily Anthropized Area
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water Article Variability in Environmental Conditions Strongly Impacts Ostracod Assemblages of Lowland Springs in a Heavily Anthropized Area , , Giampaolo Rossetti * y, Valentina Pieri y z, Rossano Bolpagni , Daniele Nizzoli and Pierluigi Viaroli Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, 43124 Parma, Italy; [email protected] (V.P.); [email protected] (R.B.); [email protected] (D.N.); [email protected] (P.V.) * Correspondence: [email protected] These authors contributed equally to this work. y Present address: Iren Laboratori S.p.A., Piacenza, Italy. z Received: 6 October 2020; Accepted: 17 November 2020; Published: 21 November 2020 Abstract: The Po river plain (Northern Italy) hosts artificial, lowland springs locally known as fontanili, which provide important ecosystem services in an area dominated by intensive agricultural activities. Here we present a study carried out in 50 springs. Each spring was visited once from October 2015 to January 2016. The sampled sites were selected to include springs studied in 2001 and 2004, to evaluate changes in water quality and ostracod assemblages that possibly occurred over a period of 10–15 years, and explore the relationships between ostracod community composition and water physical and chemical variables. Our results showed a decrease in the chemical water quality especially, in springs south of the Po river, evidenced by high nitrate levels. Most of the studied springs showed a relevant decrease in dissolved reactive silica, probably related to recent transformations of either agricultural practices or crop typology. Ostracods were mostly represented by common and tolerant species, and communities were characterized by low alpha diversity and high species turnover. Water temperature and mineralization level were the most influential variables in structuring the ostracod communities. We stress the need to implement conservation and restoration measures for these threatened ecosystems, to regain their role as ecosystem services providers. Keywords: groundwater dependent ecosystems; Northern Italy; hydrochemistry; nutrient stoichiometry; non-marine ostracods; ecosystem services 1. Introduction A large number of semi-artificial, groundwater-dependent ecosystems (GDEs), locally known as “fontanili”, occur in the Po and Venetian plains (Northern Italy) along the alluvial fans and terrace deposits of watercourses in the transition zone from higher to lower plain. Across this so-called spring belt, due to changes in both terrain slope and sediment grain size [1–4], groundwater outflows through aquifers under a natural hydraulic gradient occur, which are usually further facilitated by driving perforated pipes and soil excavation. Most of the fontanili can be classified as rheo-limnocrenic springs [5]. The prevalent morphology consists of a spring area, known as “head”, which is relatively deep and where the water is almost still, and a drainage channel through which water flows downstream. In order to maintain suitable hydrological conditions, these systems require periodic management to remove the aquatic vegetation and the accumulation of organic sediment. Water 2020, 12, 3276; doi:10.3390/w12113276 www.mdpi.com/journal/water Water 2020, 12, 3276 2 of 20 Lowland springs are often described as stable habitats, with modest changes in hydrological, thermal, chemical, and biological characteristics, as they are fed by aquifers that guarantee relatively constant conditions at seasonal and interannual timescales [2,6]. The fontanili were exploited over centuries as micro-climate regulators in the lowland grassland of Lombardy. Here, until the late 1960s, in the cold season, stable meadows (locally called ”marcite”) were submerged in water from lowland springs at nearly 10–12 ◦C, a temperature much greater than the atmospheric one and sufficient to allow a slight warming and to avoid water freezing. Therefore, the productivity of such meadows was higher compared to traditional lawns. Lowland springs are components of interconnected systems of lentic waters, streams and channels, where nutrients can be removed by both aquatic vegetation and microbial processes [7,8]. They host relict (palaeo-) endemics, i.e., cold-stenotherm plants and animal taxa which underwent altitudinal displacements from mountain areas during the Würm glacial expansion, whose persistence is strictly linked to the conservation of these peculiar “ecological islands” surrounded by human-dominated landscapes [9–11]. Overall, lowland springs are refuge areas for species suffering strong declines in the study area, e.g., pike (Esox lucius)[12]. Despite their great potential value as ecosystem services providers, poor or inappropriate management practices, excessive water abstraction, land reclamation due to agricultural activities and the expansion of grey infrastructures, the spreading of alien species and the impacts of climate change on hydrology are threatening the conservation status of lowland springs [13–16]. Moreover, agriculture affects surface and groundwater quality due to the application of fertilizers that are largely in excess compared with crop uptake, resulting in a sensible increase in nutrient concentrations in most of these GDEs [17,18]. The hydrochemical and ecological features of the fontanili are relatively well studied [2,19–21], especially in the central area of the Po river plain [17,22–24]. In particular, two studies have investigated the relationships between water chemistry and ostracod assemblages [10,15]. Ostracods (class Ostracoda) are small bivalved crustaceans occurring in almost all aquatic ecosystems, mostly in benthic and periphytic habitats. According to Meisch et al. [25], there are presently 2330 subjective species of non-marine ostracods in 270 genera, all belonging to the order Pocodocopida. The Italian non-marine ostracod fauna consists of about 160 species, and it is currently the most diverse in Europe [26]. Accumulating evidence indicates that non-marine ostracods differently respond to environmental conditions, and may be used as bioindicators [27–35]. Their potential as environmental indicators has long been recognized by palaeolimnologists, who infer temporal changes in the local environment from changes in the assemblages of calcified ostracod valves [36–38]. The present research aimed at comparing the current hydrochemical status and the composition of the ostracod communities of 50 lowland springs of the Po river plain with those reported in previous studies carried out in the period 2001–2004 [10,15]. The magnitude of changes was statistically estimated using univariate methods, both between and within different sub-catchments to identify possible spatial patterns. Particular attention was paid to the trends of the stoichiometric ratios of the major dissolved nutrients. In addition, the distribution patterns and the compositional turnover of the ostracod communities over the considered time period were investigated, and the relationships between ostracod occurrence and environmental variables were evaluated by multivariate analysis. The results of this study can be used to assess the often-presumed stability of lowland springs, in terms of weak or delayed responses to anthropic disturbance in their hydrochemical and biological characteristics, and to provide insights into the potential future trajectories of these threatened ecosystems. 2. Materials and Methods 2.1. Study Area The study area encompassed 59 lowland springs belonging to nine sub-catchments of the Po river, located in five provinces: Piacenza and Parma in the Emilia-Romagna region (Apennine side of WaterWater2020 2020, 12,, 12 3276, x FOR PEER REVIEW 3 of3 20 of 20 The study area encompassed 59 lowland springs belonging to nine sub-catchments of the Po theriver, Po plain, located south in five of provinces: the Po river), Piacenza and Lodi, and Parma Cremona in the and Emilia Milano-Romagna in the region Lombardy (Apennine region side (Alpine of sidethe of Po the plain, Po plain, southnorth of the ofPo the river), Poriver) and Lodi, (Table Cremona S1, Figure and1 ).Milano Each springin the Lombardy was visited region once (Alpine between Octoberside of 2015 the Po and plain, January north 2016. of the Samples Po river) were (Table collected S1, Figure from 1). each Each active spring spring, was visited 29 in Emilia-Romagna once between (identifiedOctober 2015 with and the codesJanuary “PC” 2016. and Samples “PR” followedwere collected by a number)from each and active 21 inspring, Lombardy 29 in (codeEmilia- “S” followedRomagna by (identified a number). with All the the codes sampled “PC” sites and were“PR” followed also included by a number) in the studies and 21 byin Lombardy Rossetti et (code al. [10 ] and“S” Pieri followed et al. [by15 a] onnumber). springs All in the Emilia-Romagna sampled sites were and also Lombardy, included respectivelyin the studies (same by Rossetti site codes et al. as [10] and Pieri et al. [15] on springs in Emilia-Romagna and Lombardy, respectively (same site codes above). In Rossetti et al. [10], sampling took place between May and August 2001, and each spring as above). In Rossetti et al. [10], sampling took place between May and August 2001, and each spring was sampled once; in Pieri et al. [15], each spring was sampled twice, in summer (late June–early was sampled once; in Pieri et al. [15], each spring was sampled twice, in summer (late June–early September) and autumn (November) 2004. September)